Generally, liquid crystal is easily influenced by external stimulation such as an electric field, a magnetic field, stress, etc. As a result of this characteristic, the liquid crystals can be applied to a light shutter and even to a display device.
In order to utilize this characteristic of liquid crystal, the liquid crystal molecule can be moved as desired according to the change of the external environment. Therefore, the uniform orientation of the liquid crystal is important.
An organic layer coated and orientation treated on the transparent electrode interacts physicochemically with liquid crystal by the bonding energy such as van der Waals force, attraction between dipoles, hydrogen bonding, etc. This is known to be the main factor of liquid crystal orientation (see "Liquid Crystal Application and Uses," Vol. 3, 1992, World Scientific Publishing Co.). In addition, micro-grooves formed on the organic layer during rubbing using a rubbing cloth are another factor of liquid crystal orientation.
In order to orient liquid crystalline material during the manufacture of the liquid crystal display device according to the conventional method, an organic layer, preferably a polyimide layer, is coated on the transparent electrode formed on the substrate. Then, the organic layer is rubbed using a cloth to orient the liquid crystal molecule to the rubbing direction or perpendicular thereto (Japanese Patent Laid-open Publication No. sho 63-14122). However, the organic layer is damaged by the rubbing cloth during the rubbing treatment which induces nonuniform orientation of the liquid crystal and causes other defects which adversely affect the manufacture of the liquid crystal display device.
If the liquid crystal is injected after such mechanical rubbing, nonuniform orientation due to rubbing traces (i.e., variations in the size and depth of the grooves and other contaminant) is produced, which ultimately causes significant damage to the electric-optic effect of the liquid crystal. Here, bistability, which is a particularly important property of ferroelectric liquid crystal, becomes erratic and the memory characteristic of the liquid crystal is deteriorated (see Japanese Patent Laid-open Publication Nos. hei 1-155318, hei 1-281428 and hei 2-61614). In addition, dust produced after the mechanical rubbing reacts directly with the liquid crystal to break the orientation and to induce various other defects (see Japanese Patent Laid-open Publication Nos. sho 63-132220 and hei 3-59089).
Particularly, for the ferroelectric liquid crystal, the disruption of orientation is easily induced, even by a trivial defect. In this case, since good bistability cannot be easily obtained, a liquid crystal display device exhibiting good bistability characteristics cannot be easily manufactured.